The present invention relates to an image forming apparatus.
Conventionally, in an image forming apparatus adopting an electrophotographic form, a photoconductor that is an image bearing member is charged by a charger, the charged photoconductor is irradiated with light according to image data to form a latent image thereon, this latent image is developed by a developing device, and the developed toner image is transferred onto a recording medium, whereby an image is formed.
On the other hand, with colorization of image, a tandem type color image forming apparatus is also proposed, in which plural image forming units executing such each image forming process are provided, toner images of cyan, magenta, yellow, and preferably black are formed on the respective photoconductors, and these toner images are multi layer transferred onto an endless intermediate transfer member in a transfer position of each photoconductor, whereby a full color image is formed.
Since such the tandem type color image forming apparatus has an image forming section for each color, it is advantageous for speed-up.
A conventional tandem type color image forming apparatus will be described below.
FIG. 7 is a schematic view showing the constitution of the conventional color image forming apparatus. FIG. 8 is a perspective view in which a first gear portion 315 used in a photoconductor drum of the conventional color image forming apparatus is partially broken.
In FIG. 7, in a body 1 of the color image forming apparatus, image forming units 2, 3, 4 and 5 for forming respectively toner images of each color of yellow (Y), magenta (M), cyan (C), and black (K) are arranged, and exposing devices 6a, 6b, 6c, and 6d respectively corresponding to these image forming units 2 to 5 are provided. The image forming units 2 to 5 include photoconductor drums (photoconductors) 2a, 3a, 4a, and 5a on peripheral surfaces of which electrostatic latent images are formed by irradiation of laser beams from the exposing devices 6a to 6d; and developing rollers 2b, 3b, 4b, and 5b (developing units) which attach toner supplied from toner tanks onto the photoconductor drums 2a to 5a to make the electrostatic latent images visible as toner images.
On the lower sides of the image forming units 2 to 5, an endless intermediate transfer belt (intermediate transfer member) 7 on which a color toner image is formed by multi layer transferring the toner images of the respective colors made visible on the photoconductor drums 2a, 3a, 4a, and 5a is arranged so that it can run in the direction of an arrow. The intermediate transfer belt 7 includes a drive roller 8, a tension roller 9, four first bias transfer rollers 10a, 10b, 10c and 10d, and a driven roller 11 in its loop.
At the lower portion of the apparatus, a paper supply cassette 13 storing paper (recording medium) P therein is provided. The paper P is fed out from the paper supply cassette 13 to a paper transport path one by one by a supply roller.
On the paper transport path, a second bias transfer roller 12 which comes into contact with the peripheral surface of the intermediate transfer belt 7 by the predetermined amount in the position of the driven roller 11 thereby to transfer the color image on the intermediate transfer belt 7 onto the paper P, and a fixing device 14 which fixes the color image transferred onto the paper P onto the paper P are arranged.
In the thus structured image forming apparatus, onto the surface of the intermediate transfer belt 7, the toner images of yellow, magenta, cyan and black adhere from the photoconductor drums 2a to 5a in the image forming units 2 to 5 and the color image is formed. This toner color image is transferred onto the paper P taken out of the sheet supply cassette 13 by the nip power between the driven roller 11 and the second bias transfer roller 12. Then, the paper P is supplied to the fixing device 14, the toner image is fixed thereon, and thereafter the paper P is exhausted.
Here, as shown in FIG. 8, at the inner surrounding of one end of each of the photoconductor drums 2a to 5a, a first gear portion 315 having plural teeth 315a extending axially is formed on the axis of rotation. Further, at the outer surrounding of the photoconductor drive shaft, a second gear portion engaging with this first gear portion 315 is formed on the axis of rotation. By the first gear portion 315 and the second gear portion, each photoconductor drum 2a to 5a and each photoconductor drive shaft gear with each other on the same axis, so that each photoconductor drum 2a to 5a is rotation-driven by each photoconductor drive shaft. Such the rotation-drive and gear constitution have been disclosed in, for example, US Pub. No. 2002/0085858A1, U.S. Pat. No. 6,285,847 B1, and JP-A-2000-352898.
However, when each image forming unit 2 to 5 is attached to the image forming apparatus body, in case that the first gear portion 315 on the photoconductor drum 2a to 5a side and the second gear portion on the photoconductor drive shaft side are in the same phase, the leading ends of their teeth come into contact with each other, so that the photoconductor drive shaft is not inserted into the photoconductor drum 2a to 5a. 